The production of composite components often uses polymer compositions which are based, for example, on unsaturated polyester resins (UP resins) and which are capable of free-radical crosslinking. Unsaturated polyester resins are obtainable via polycondensation of dicarboxylic acids or of dicarboxylic anhydrides with polyols. The polymer compositions capable of free-radical crosslinking also comprise monomers having ethylenically unsaturated groups, generally styrene. By way of example, styrene is added to the polymer composition capable of free-radical crosslinking in order to dissolve the crosslinkable polymer and to ensure that the polymer composition capable of free-radical crosslinking is flowable. Other constituents often present in the polymer compositions capable of free-radical crosslinking are fiber materials, such as glass fibers, carbon fibers, or corresponding fiber mats (Fiber Reinforced Plastic composites=FRP composites), where these lead to reinforcement of the composite components obtainable via hardening of the polymer compositions capable of free-radical crosslinking.
A problem that occurs when these polymer compositions capable of free-radical crosslinking are processed to give composite components is volume shrinkage during the curing of the polymer composition. The materials known as low-profile additives (LPAs) are therefore added to the polymer compositions capable of free-radical crosslinking, in order to reduce shrinkage during hardening. Low-profile additives reduce shrinkage during hardening, dissipate intrinsic stresses, reduce microcracking, and facilitate compliance with manufacturing tolerances. The low-profile additives usually involve thermoplastics, such as polystyrene, polymethyl methacrylate, and in particular polyvinyl acetate, and these often also comprise carboxy-functional comonomer units. Corresponding low-profile additives based on vinyl acetate and on ethylenically unsaturated carboxylic acids are described by way of example in U.S. Pat. No. 3,718,714 or DE-A 102006019686.
Copolymers based on vinyl acetate and styrene have also been described as LPAs for unsaturated polyester resins. By way of example, EP-A 0414468 has disclosed UP resins where A-B block copolymers are added as LPAs, where the A block is composed of vinyl acetate and butyl acrylate, and the B block is composed of styrene or of copolymers thereof. However, it is necessary to use specific polymeric peroxides for the hardening of these UP resins. The patents GB 2087416 and U.S. Pat. No. 4,303,762 also describe UP resins with use of block copolymers made of vinyl acetate copolymers and styrene copolymers as LPAs. Here again, specific polymeric peroxides are used in the hardening process.
DE-A 102007055694 discloses polymers which are obtained via polymerization of vinyl esters and of ethylenically unsaturated epoxy-functional monomers and subsequent polymer-analogous reaction of the resultant polymers with an ethylenically unsaturated carboxylic acid. DE-A 102007055694 describes the hardening of the polymers via free-radical-initiated polymerization, and also the use of the polymers as LPAs.
However, the LPA effect of the polymers described is apparent only during the curing of crosslinkable polymer compositions at elevated temperatures. The LPAs commonly used exhibit no, or inadequate, effectiveness at room temperature. However, there are many processes for producing composite components where the hardening of the crosslinkable polymer compositions specifically takes place at low temperatures, for example at room temperature: examples are the hand-lay-up process or infusion processes or injection processes, for example vacuum infusion, or resin transfer molding (RTM).